Relationship between quadriceps strength and bone mineral density of the proximal tibia and distal forearm in women

It is well known that there is a relationship between muscle strength and bone density, but it is uncertain whether this relationship is site specific. The aim of this study was to assess the relationship of quadriceps strength to site-specific bone mineral density (BMD) of the tibia and to BMD of the forearm. In 66 healthy women, aged 21-78 years, BMD was measured in the proximal tibia and the distal forearm by dual-photon absorptiometry. Isometric and isokinetic strength of the quadriceps was measured using an isokinetic dynamometer (Cybex II). Highly significant correlations between BMD of the proximal tibia and quadriceps strength were found (RS ranging from 0.79 to 0.84, p < 0.0001). Also, BMD of the distal forearm was correlated with quadriceps strength (RS ranging from 0.59 to 0.62, p < 0.0001). In a stepwise multiple regression analysis, quadriceps strength was a better predictor of tibial BMD than age, body height, or weight. However, age, height, and weight were more predictive of forearm BMD than quadriceps strength. When studying the pre- and postmenopausal women separately, quadriceps strength was correlated with BMD of the proximal tibia but not to forearm BMD. In conclusion, the study provides support for a site-specific relationship between muscle and bone.